Twenty-five personnel were at the site, including Search and Rescue specialists from the Canterbury Police and Alpine Cliff Rescue, together with geotechnical specialists and representatives Mines Rescue and WorkSafe New Zealand.

They could see the arm of the digger but attempts to contact the driver had been unsuccessful, Mr Parnell said.

"It may well be an operation where we use remote capability, which we saw during the Christchurch earthquakes," he said.

"Again, that's all options we're exploring at the moment.

"I can't express enough, in terms of the instability up there at the front end."

Victim Support was working with the man's family, Mr Parnell said.

Hurunui District Council owns the land the quarry is on and chief executive Hamish Dobbie said it was shaken by the incident.

Details of the accident remained unclear but the council would co-operate with all investigations.